# microbenchmark

0th

Percentile

##### Sub-millisecond accurate timing of expression evaluation.

microbenchmark serves as a more accurate replacement of the often seen system.time(replicate(1000, expr)) expression. It tries hard to accurately measure only the time it takes to evaluate expr. To achieved this, the sub-millisecond (supposedly nanosecond) accurate timing functions most modern operating systems provide are used. Additionally all evaluations of the expressions are done in C code to minimize any overhead.

##### Usage
microbenchmark(..., list = NULL, times = 100L, unit, check = NULL,
control = list())
##### Arguments
...

Expressions to benchmark.

list

List of unevaluated expression to benchmark.

times

Number of times to evaluate the expression.

unit

Default unit used in summary and print.

check

Function to check if the expressions are equal. By default NULL which omits the check.

control

List of control arguments. See Details.

##### Details

This function is only meant for micro-benchmarking small pieces of source code and to compare their relative performance characteristics. You should generally avoid benchmarking larger chunks of your code using this function. Instead, try using the R profiler to detect hot spots and consider rewriting them in C/C++ or FORTRAN.

The control list can contain the following entries:

order

the order in which the expressions are evaluated. “random” (the default) randomizes the execution order, “inorder” executes each expression in order and “block” executes all repetitions of each expression as one block.

warmup

the number of warm-up iterations performed before the actual benchmark. These are used to estimate the timing overhead as well as spinning up the processor from any sleep or idle states it might be in. The default value is 2.

##### Value

Object of class ‘microbenchmark’, a data frame with columns expr and time. expr contains the deparsed expression as passed to microbenchmark or the name of the argument if the expression was passed as a named argument. time is the measured execution time of the expression in nanoseconds. The order of the observations in the data frame is the order in which they were executed.

##### Note

Depending on the underlying operating system, different methods are used for timing. On Windows the QueryPerformanceCounter interface is used to measure the time passed. For Linux the clock_gettime API is used and on Solaris the gethrtime function. Finally on MacOS X the, undocumented, mach_absolute_time function is used to avoid a dependency on the CoreServices Framework.

Before evaluating each expression times times, the overhead of calling the timing functions and the C function call overhead are estimated. This estimated overhead is subtracted from each measured evaluation time. Should the resulting timing be negative, a warning is thrown and the respective value is replaced by 0. If the timing is zero, a warning is raised. Should all evaluations result in one of the two error conditions described above, an error is raised.

One platform on which the clock resolution is known to be too low to measure short runtimes with the required precision is Oracle Solaris on some SPARC hardware. Reports of other platforms with similar problems are welcome. Please contact the package maintainer.

print.microbenchmark to display and boxplot.microbenchmark or autoplot.microbenchmark to plot the results.

##### Aliases
• microbenchmark
##### Examples
# NOT RUN {
## Measure the time it takes to dispatch a simple function call
## compared to simply evaluating the constant \code{NULL}
f <- function() NULL
res <- microbenchmark(NULL, f(), times=1000L)

## Print results:
print(res)

## Plot results:
boxplot(res)

## Pretty plot:
if (require("ggplot2")) {
autoplot(res)
}

## Example check usage
my_check <- function(values) {
all(sapply(values[-1], function(x) identical(values[[1]], x)))
}

f <- function(a, b)
2 + 2

a <- 2
## Check passes
microbenchmark(2 + 2, 2 + a, f(2, a), f(2, 2), check=my_check)
# }
# NOT RUN {
a <- 3
## Check fails
microbenchmark(2 + 2, 2 + a, f(2, a), f(2, 2), check=my_check)
# }

Documentation reproduced from package microbenchmark, version 1.4-4, License: BSD_2_clause + file LICENSE

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